ALSA: usb-audio: fix OOB write in snd_usbmidi_novation_output()

Overview

In the Linux kernel, the following vulnerability has been resolved:

ALSA: usb-audio: fix OOB write in snd_usbmidi_novation_output()

snd_usbmidi_novation_output() lays out a two-byte header at transfer_buffer[0..1] and passes &transfer_buffer[2] together with a length of ep->max_transfer - 2 to snd_rawmidi_transmit():

count = snd_rawmidi_transmit(ep->ports[0].substream,
			     &transfer_buffer[2],
			     ep->max_transfer - 2);

ep->max_transfer comes from the output endpoint's wMaxPacketSize via usb_maxpacket(). A malformed or malicious device can advertise a bulk OUT endpoint with a wMaxPacketSize of 1 - the USB core only clamps this value downwards - so ep->max_transfer becomes 1 and the count argument becomes -1.

snd_rawmidi_transmit() passes the negative count on to __snd_rawmidi_transmit_peek(), where "if (count1 > count) count1 = count" leaves count1 negative; get_aligned_size() keeps it negative for a byte-stream substream, so the following memcpy(buffer, ..., count1) runs with a (size_t)-1 length and writes far past the transfer buffer, which was allocated with usb_alloc_coherent(ep->max_transfer).

This is the same class of bug that was fixed for snd_usbmidi_akai_output() in commit 0970274613fb ("ALSA: usb-audio: fix OOB write in snd_usbmidi_akai_output()"); the novation output routine was left unguarded. Bail out when the endpoint cannot hold the two-byte header plus at least one payload byte.

Affected

• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 558fc4485ecc704edfe7876d6cebae4738ff7ef8
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 9c8212436631b0063cb021e9f58df438e3db84d0
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < e9c00d7533f99aa9833c4b598f47e3b3202fdb9a
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 94e4562fcc81badd1d467ddfb88c27e4fae974c2
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 7639ec9755d3ec0ec8cd7c0fdd2c3d3997434870
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 91919b3b99ab7ce3d7dbb39fcf7c6c742a663c0c
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 7f00dbddb51f4f74325cdc7c3f6b19fb3392481a
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 1074c2306901b44ebcb83855583c6776e1e392ea
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 1035a8f63bae28e498b0e7b5ac91d749844a7158
• Linux 2.6.12

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.